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The Nervous System
Function: The nervous system controls and coordinates the functions throughout the
body and responds to external and internal Stimuli.
Name:
Class period:
Chapter 35
Parts of the Brain
The Cerebrum • The largest area of the brain• Responsible for the voluntary or conscious activities
of the body• The site of intelligence, learning and judgment• Divided by a deep groove into the right and left
hemispheres• Connected by the Corpus Callosum, band of tissue• Fold and grooves on surface- increase surface area• Made up of two layers
Cerebral Cortex
• Cerebral cortex-outer layer made up of gray matter (densely packed nerve cell bodies)
• Processes information from the sense organs and controls body movements
Inner Cerebrum
• Inner layer is made up of white matter• Bundles of axons with myelin sheaths• Myelin is a lipid layer that gives white matter
its color• White matter connects the cerebral cortex
and the brain stem
The Cerebellum
• Second largest region of the brain• Located at the back of the skull• Coordinates and balances the actions of the
muscles so that the body can move gracefully and efficiently
Brain Stem
• Connects the brain and the spinal cord• 2 Regions-
– Pons and Medulla Oblongata• Act as neural “switchboard” regulating the flow
of info between the brain and the rest of the body
• Medulla Oblongata is responsible for body’s important functions-blood pressure, heart rate, breathing, swallowing- Involuntary Actions
Thalamus• Found between the brain stem and cerebrum• Receives messages from all of the sensory
receptors throughout the body and relays that information to the proper region of the cerebrum for processing
Thalamus (red) & Hypothalamus (bright orange/yellow)
Hypothalamus• Sits just below the thalamus
(hypo- under)• Control center for
recognition and analysis of hunger, thirst, fatigue, anger and body temperature
• Maintains homeostasis/ equilibrium in the body
• Coordination of the nervous and endocrine systems
Spinal Cord
• Main communication link between brain and rest of body
• 31 pair of spinal nerves branch out from spinal cord connecting brain to all of the diff. parts of body
• Certain kinds of information, including some reflexes, are processed directly in the spinal cord
Spinal nerve
Central canalGray matter
White matter
Meninges
Section 35-3
Cross Section of the Spinal CordThe Spinal Cord
Neurons/Nerve Impulses/Synapses
Pg. 2
Axon terminals
Myelin sheath
nodes Axon
Cell body
Nucleus
Dendrites
Neuron
Neurons- specialized cells that carry messages by transmitting electrical signals throughout the
nervous system
Types of neurons:1. sensory- carry impulses from the sense
organs to the spinal cord and brain.2. motor- carry impulses from the brain and
spinal cord to muscles and glands.3. interneurons- connect sensory and motor
neurons and carry impulses between them.
sensory neurons-sensory neurons-
motor neurons-motor neurons- InterneuronInterneuron
Structure of neurons:1. cell body- largest part, contains the nucleus & most of the
cytoplasm; most metabolic activity of the cell takes place here 2. dendrites- short, branched extensions that spread out from
cell body; carries impulses from the environment/other neurons toward the cell body.
3. axon- long fiber that carries impulses away from the cell body.4. myelin sheath- insulating membrane around an axon. Gaps in
between sheaths are called nodes5. Axon terminals- the branched part of the axon at the end
Neurons
• Neurons may have many dendrites but only one axon
• Neurons are clustered into bundles called nerves, a few to thousands bundled
• Myelin Sheath-insulating membrane with gaps called nodes, area with no myelin
• Impulse jumps at nodes increasing the speed of passage
Nerve Impulse- an electrical impulse conducted along a nerve fiber.
1. resting potential- the neuron is not transmitting an impulse, and the electrical charge across the cell membrane of a neuron is in its resting state. The outside of the cell has a net positive charge, and the inside of the cell has a net negative charge.
2. action potential- the reversal of charges, from negative to positive- called a nerve impulse; begins when a neuron is stimulated by another neuron or by the environment- impulse travels rapidly away from cell body and moves toward axon terminals and into the synapse.
3. threshold- the minimum level of stimulus that is required to activate a neuron -All or None- either there is an impulse or there is not- strength of an impulse is always the same
The Synapse & Neurotransmitter
• Synapse: the location at which a neuron can transfer an impulse to another cell
• Neurotransmitter: chemicals used by a neuron to transmit an impulse across a synapse to another cell
The Central Nervous System (CNS)
• Main functions of the CNS: 1st conveys messages between brain and spinal cord; 2nd processes info, problem solving
• 2 structures make-up the CNS:1- brain 2- spinal cord
• The job for these 2 structures is to respond to the environment
The Central Nervous System (CNS) cont.
• 3 protective mechanisms:– the skull and vertebrae– The structures are wrapped in meninges
(connective tissue) & it consists of 3 layers (protection)
– Cerebral spinal fluid (CSF):1st bathes brain and spinal cord -2nd shock absorber that protects CNS -3RD allows for exchange of nutrients and waste products between blood and nervous tissue
Peripheral Nervous System• Function: receives info. from the environment
and relays commands from the CNS to organs and glands
• It lies OUTSIDE the CNS • Includes all nerves and associated cells that are
not part of the brain and spinal cord• divided into sensory & motor divisions
– Motor: transmits impulses from the CNS to muscles or glands
• Motor can be further divided into:– Somatic Nervous System– Autonomic Nervous System
– Sensory: transmits impulses from sense organs to the CNS
• (own notes on sensory receptors pg. 906)
Motor division-Somatic Nervous System (SNS)
Pg. 5
Somatic Nervous System (SNS)• regulates activities that are under conscious control• Movement of skeletal muscles• Some somatic nerves involved with reflexes & can
act with or without conscious control
Pg. 5
How a reflex works (reflex arc)• Stimulus:1. step on tack2. stimulates sensory receptors/sensory neurons
in foot 3. impulse travels via sensory neuron to spinal
cord4. spinal cord neurons (interneurons) activate
motor neurons5. impulse travels via motor neuron to muscle6. muscles in foot contract, pulling foot away
(effector muscle= muscle that is moving) **All of this takes only a fraction of a second
Pg. 5
Motor division-Autonomic Nervous System (ANS)
Pg. 6
Autonomic Nervous System (ANS)
• Regulates activities that are automatic/involuntary
• Nerves of ANS control functions not under conscious control
• Controls other body systems – ex: when you run, the ANS:
1. increase heart rate and blood flow to skeletal muscles
2. stimulates sweat glands and adrenal gland 3. decrease contractions of smooth muscle in digestive
system
Pg. 6
Autonomic Nervous System (ANS) cont
• Divided into 2 sections: 1. Sympathetic-increase heart rate (think “gas
pedal”) 2. Parasympathetic-decrease heart rate (think
“brakes”)
• Opposite effect on organs- help body maintain homeostasis
• *most organs controlled by both
Pg. 6
III. The Senses
A. Sensory receptors- are neurons that react to stimuli in the environment. These receptors send impulses to the central nervous system.1. 5 types of sensory receptors:
a. pain receptors- respond to pain. b. thermoreceptors- respond to
temperature. c. mechanoreceptors- respond to pressure.
d. chemoreceptors- respond to chemicals. e. photoreceptors- respond to light.
Choroid
Retina
Blood vessels
Optic nerve
Fovea
Vitreous humor
Sclera
Ligaments
Iris
Pupil
Cornea
Aqueous humor
Lens
Muscle
Section 35-4
Figure 35-14 The Eye
Auditory canal
Tympanum Round window Eustachian tube
Bone
Cochlea
Cochlear nerve
Semicircular canals
Oval window
StirrupAnvilHammer
Section 35-4
Figure 35-15 The Ear
Cerebral cortex
Nasal cavity
Taste bud
Smell sensory area
Tastesensory area
Thalamus
Olfactory(smell) bulb
Olfactorynerve
Smell receptor
Taste pore
Taste receptor
Sensorynerve fibers
Section 35-4
The Senses of Smell and Taste
Drugs & the Nervous System:• A drug is any substance, other than food,
that changes the structure of function of the body
3 ways that drugs affect the body:1. Kill bacteria and useful in treating diseases2. Some affect a particular system
• Digestive• Circulatory
3. MOST POWERFUL are the ones that cause changes in the NS, especially to the brain and the synaptic gaps (between the neurons)
The following are drugs that affect synaptic gaps or neurotransmitters:
Stimulants (such as amphetamines, cocaine, nicotine & caffeine)– Medical uses are to increase alertness & relieve fatigue– They increase actions regulated by the nervous system– They increase heart rate, respiratory rate, blood
pressure, breathing rate, dilates pupils and decreases appetite.
– They increase the release of neurotransmitters at some synapses in the brain.
Depressants: (such as Barbiturates & tranquilizers)
• Medical uses are to relieve anxiety, irritability & tension
• They decrease the rate of functions regulated by the brain & slows actions of CNS
• They decrease heart rate, blood pressure & breathing rate
• Small amounts cause calmness & relaxation; Large amounts cause slurred speech & impaired judgment
• NOTE: if used with alcohol, can depress CNS so much that breathing STOPS!!!
Cocaine:• Causes a sudden release in the neurotransmitter dopamine
(usually released normally when a basic need- such as hunger or thirst- is fulfilled). This produces intense feeling of pleasure & satisfaction. HOWEVER, since so much is released so quickly, dopamine amounts are depleted and when the drug wears off, intense sadness and depression occurs, causing psychological dependency. (Crack is an even more potent form of cocaine causing even more intense symptoms and quicker dependency)
• Also a powerful stimulant that increases heart rate & blood pressure which can lead to heart damage or heart attack
Opiates: (such as Morphine, codeine & oxycotin)• Medical uses are to relieve pain• These mimic natural chemicals in the brain known
as endorphins, which help to relieve pain• These act as depressants causing drowsiness,
restlessness & nausea• Drug produces strong feelings of pleasure and
security, but the body quickly adjusts and needs higher levels each time to achieve same feelings: EXTREMELY ADDICTIVE!
• A user who tries to stop taking these will suffer uncontrollable pain, sadness & sickness because the body can not produce enough natural endorphins.
Marijuana• Tetrahydrocannabinol (THC) active ingredient• Most widely abused illegal drug!
